A camera is mounted on a mobile phone or any other portable terminals, and cost reduction of an image pickup lens attached to the camera is being required. In order to satisfy such a request, only a review of each process on the basis of an existing manufacturing method has limitation, and the increase in efficiency through a series of process design is required. Furthermore, thickness reduction is required as a market trend, and a request for thickness reduction of a lens which is a component to be mounted thereon is inevitably increasing. A method for satisfying such a request is considered to include a method of forming a lens array made of glass through pressing to thereby be divided into individual lenses, and is considered to be advantageous in that a large number of small-sized glass lenses can be produced with relatively high accuracy at one time.
As a manufacturing method of a lens array made of glass, a glass mold method is known. Here, the glass mold method refers to a method of obtaining an optical element such as a lens as an integral product made of glass by pressing heated and softened glass on a transfer surface of a pair of molding die and by cooling it. As a manufacturing method of a lens array by such a glass mold method, a method of press-molding glass in which a top of an outer-edge flange portion is formed on an outside of a thin flange portion adjacent to an optical fictional surface so that the top of the outer-edge flange portion becomes slightly higher than the top of the optical functional surface and in which a projection portion for preventing inflow of an adhesive into the optical functional surface is formed on the outer-edge flange portion is known (Patent Literature 1). A die used in this method includes a core for molding the optical functional surface and the flange portion and is obtained by subjecting a tip end of a core fitting hole to which the core is fitted to inclination machining, and thus the projection portion is formed on the outer-edge flange portion by transferring a shape of a groove portion formed by the inclination machining.
As another manufacturing method of a lens array made of glass, a method of molding a lens sheet having a large difference between a thickness of a lens portion and a thickness of an edge portion by re-heating a glass material machined into a plate shape by a die is known (Patent Literature 2). In this method, a lens sheet in which the lenses are aligned in a lattice shape is manufactured by using a die in which a glass-material reservoir portion that is a semispherical dent is provided at a center part, by sandwiching a glass material sheet between the dies, and by softening and pressing the glass material sheet through heating. The lens sheet molded as described above is divided into individual pieces by being cut to thereby give a glass lens.
As another manufacturing method of a lens array made of glass, a method of molding a thin-plate shaped micro lens array by heating and softening glass preform is known (Patent Literature 3). In this method, a concave portion referred to as a nest cavity is provided close to a center in a die, the preform is arranged in this concave portion, and a gas is discharged from a lens cavity in the die as the glass flows out toward the outside from the center when being pressed and thus the micro lens array having provided a lens portion with an accurate surface shape can be formed. The micro lens array molded as described above is divided into individual pieces by being cut to thereby give a micro lens made of glass.
However, positioning when the lens array is fixed to another component (another lens array, for example) is not easy in the case of using the lens array obtained by Patent Literature 1. In Patent Literature 1, the outer-edge flange portion is provided in order to adjust an interval between facing lenses, but an alignment function relating to a direction perpendicular to an optical axis cannot be expected. That is, the projection portion provided on the outer-edge flange portion is not easily formed with accuracy since glass is forced to enter a gap having a wedge-shaped section provided between the core and the core fitting hole, and two lens arrays cannot be precisely positioned even by using this projection portion.
Furthermore, the lens arrays obtained by Patent Literatures 2 and 3 cannot be easily positioned when the lens array is fixed to another component (for example, another lens array). The glass-material reservoir portion is provided in Patent Literature 2 and the nest cavity is provided in Patent Literature 3, but a function of mutually aligning the arrays in these convex shapes cannot be found.
In addition, as to the lens array made of glass, a molding area becomes large since a large number of lenses are molded at one time, and condition modification such as increase in a molding pressure is required at the time of molding. Therefore, risks such as lens breakage, lens warpage, damage to a die, glass adhesion (occurrence of fusion) become higher. Particularly, although a droplet molding method of a type in which a glass droplet is received by a die and is pressed enables rapid and precise pressing, problems such as lens breakage, lens warpage and the like as described above become easily apparent along with a size increase in the lens array.